The known examples of frame synchronization include the following techniques (refer to Patent Document 1).
Patent Document 1 discloses the following frame synchronous system.
In TDMA (time-division multiplex access) system, a plurality of wireless stations time-divisionally uses one radio frequency. In the TDMA system, a sound signal is converted into a digital signal, and subsequently a speed conversion is additionally performed, thereby transmitting the signal to a time slot which is assigned to the corresponding station. Reception is performed in a way that a reverse speed conversion is performed on the signal of the time slot assigned to the corresponding station, the digital signal is reconverted into the analog sound signal, and the reconverted signal is output.
On the other hand, when a mobile station moves and enters into a service area (zone) of another wireless base station, sometimes TDMA frame synchronization is not established. In this case, in response to a received signal from the wireless base station of the destination, frame synchronization should be reestablished in accordance with synchronization establishment procedure. However, communication is cut off until synchronization is reestablished.
In contrast, when TDMA frame synchronization is established, communication can be continuously performed without execution of the synchronization establishment procedure. Accordingly, in order to prevent communication black out, it is necessary to always maintain establishment of TDMA frame synchronization between wireless base stations adjacent to each other without a large equipment.
Therefore, even when the mobile station moves to the adjacent zone, it is necessary to establish synchronization between TDMA frames transmitted from the wireless base stations in order to continuously perform transmission and reception between the mobile station and the wireless base station of the adjacent zone.
Accordingly, a reference wireless base station BSR which is a time reference is provided to transmit a reference TDMA frame. With such a configuration, each wireless base station generates a TDMA frame on the basis of the time reference which is generated by slave synchronization to the reference TDMA frame, and transmits and receives signals to and from the mobile station in the corresponding zone on the basis of the frame, thereby performing continuous communication without executing the synchronization establishment procedure even when the mobile station moves to the adjacent zone.
Patent Document 1 also discloses the following frame synchronous system.
In the system, a service area is divided into a plurality of zones, and each zone has a wireless base station BS. Each wireless base station has a standard electric-wave receiver capable of receiving a standard wave in mobile communication network for mutually transmitting and receiving signals on the basis of a TDMA system and a mobile station MS in the corresponding zone where a wireless link is established. Each wireless base station is configured to generate a TDMA frame by using the received signal, which is transmitted when a time signal preset by the standard wave receiver is received, as a time reference and to establish TDMA frame synchronization between the zones.
In the frame synchronization, which is the related art of the invention, between the receiver and the base station of PHS based on the TDD/TDMA system, the base station performs intermittent transmission on the basis of the TDD/TDMA system, and the receiver decodes the received timing while delaying time little by little, thereby searching an intermittently transmitted CCH of the base station. In this method the frame synchronization is performed.
Patent Document 1: Japanese Unexamined Patent Application Publication No. H05-300078